Restenosis, a major limitation of percutaneous transluminal coronary angioplasty procedures, can be effectively treated by intravascular radiation therapy. Radiation sources currently used for this purpose, however, produce emissions either too penetrating (iridium- 192) or not penetrating enough (strontium-90/yttrium-90 and phosphorus-32) to qualify as ideal. In the former, radiation safety of patient and personnel is an issue, in the latter absorption by arterial plaque or stent wires impacts efficacy. The solution is a radiator with intermediate properties. One such is the high-activity bremsstrahlung-enhanced thulium-170 source Implant Sciences proposes to develop. By making direct use of thulium's native x- and gamma-rays and converting the isotope's beta emissions to supplemental bremsstrahlung, a safe source minimally affected by plaque is obtained. In addition to overcoming the technical negatives of present practices, thulium-based sources, because the source material is inexpensive and readily made, promise the economic advantage of reduced cost. PROPOSED COMMERCIAL APPLICATION: Not available